tests: fix style issue of importing order in test-lock.py test-lock.py is excluded in test-check-module-imports.t, because import-checker.py reports that some stdlibs are imported after local silenttestrunner module. I can not found out any reason why tests/silenttestrunner.py should be imported before some stdlibs from the point of functionality view.

--- a/tests/test-lock.py	Mon Oct 08 10:10:06 2018 +0900
+++ b/tests/test-lock.py	Mon Oct 08 10:45:36 2018 +0900
@@ -2,11 +2,12 @@
 
 import copy
 import errno
-import silenttestrunner
 import tempfile
 import types
 import unittest
 
+import silenttestrunner
+
 from mercurial import (
     encoding,
     error,